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An automated measurement and control system has been developed for studying physiological responses of animals to thermal environment. The controlled environmental variables include air temperature (Ta,SP 0.2 C), relative humidity (RHsp 2%), and air velocity (Vsp 0.1 m.s -1 ). The measured physiological variables include surface temperature using an infrared (IR) thermal imager (0.06C sensitivity) and deep body temperature (0.1C) using a surgery-free, 4-channel telemetric device. The desired thermal conditions are realized by operating a small wind tunnel (V = 0 to 1.5 m s -1 ) inside a Ta and RH-controlled environmental room (5 L 3.5 W 3.0 H m). Near the mid section of the wind tunnel is the animal area. Auxiliary heaters (1.5 kW max each) and humidifiers are controlled to operate in stages to achieve the target set points Ta,SP and RHSP. The IR camera is interfaced to a PC via RS232 that automatically controls the timed recording of the thermal images onto a PCMCIA memory card (40MB capacity). The real-time body temperature data are displayed on a PC monitor and saved to the PC hard drive. A programmable measurement and control data logger is used for the environmental control and measurements. A video recording (VR) system is used to record the behavior of the experimental animals. The system was used to quantify the efficacy of partial surface wetting for alleviating laying hens of heat stress under various Ta (warm to hot), vapor pressure deficit (low to high) and V (calm to drafty) conditions.